Antibodies (specifically, IgGs) have garnered media attention as indicators of immunity against the SARS-CoV-2 virus and have become a daily topic of conversation among the general population. Studies such as seroprevalence in Spain, serological tests and rapid tests, plasma therapy of patients recovered from COVID-19 and immunity passports criticized revolve around these proteins present mainly in the blood (although they are also found in other biological fluids).
Laboratories and States invest billions and launch into mass production of experimental vaccines without certainty about their efficacy
Despite their great role, the truth is that antibodies are only a small part of the extremely complex and sophisticated immune system. Within the diverse defensive team against the coronavirus, there are elements with equal and even greater importance than antibodies. To the extent that some of the members of this team reflect immunity against coronavirus much better.
If this is so, why is all the testing of the general population focusing on antibodies to study immune protection? Because, today, there are no simple, cheap and rapid tests with which to identify other elements that indicate immunity with greater certainty. Only in research are more elaborate, expensive and tedious tests used to register other components of the immune system against coronavirus. The great strength of antibodies is that they can be detected easily and relatively quickly, although the information they provide us on immunity is limited.
Broadly speaking, the immune system is divided into two large response teams. Those that respond rapidly to pathogens such as viruses, but without precision or refinement, are part of the innate immune system. Specialists, who attack selectively and with great biological sophistication, appear days later in the human body alerted by the innate system, and constitute the adaptive immune system.
Innate immune system: stormtroopers
The main protagonists of the innate system that are activated after the invasion of the coronavirus in the human body are:
Interferons and proteins of the complement system
They are various proteins that behave like the "Swiss army knives" of the immune system. They are involved in a multitude of processes and increase the effectiveness of the immune system response. In the case of interferons, their name is precisely due to the ability of these molecules to interfere with the replication of viruses in infected cells and activate other antiviral defenses. These proteins are released into the blood by the cells themselves invaded by coronavirus. Unfortunately, the coronavirus has been observed to have a special ability to 'dodge' interferons and multiply while going unnoticed for longer than normal in some people. On the other hand, the complement system is made up of around 30 proteins that activate complex biochemical cascades with a multitude of functions: stimulate inflammation, make it easier for phagocytes to devour viruses, and agglutinate viral particles to prevent them from joining human cells. to infect them ...
They are various types of cells (macrophages, neutrophils, and denditric cells) that patrol the human body and have the ability to hunt down and eat coronaviruses. To do this, they surround the viruses with their cell membrane and introduce them inside, to later destroy them using enzymes and acids. They also communicate with other defense cells to alert them that there is a pathogen in the human body and present certain molecules of the coronavirus to them that serve as identification signals.
Natural killer cells (NK cells)
NK cells come into action mainly thanks to interferons. These lymphocytes check the cells of the human body to check that everything is in order. If they detect something strange in the cells, which suggests that they are infected by coronavirus, they release molecules that destroy their membranes, thus killing these cells.
Adaptive Immune System: Special Forces
The adaptive immune system is divided, in turn, into two groups: cellular and humoral immunity.
Helper T lymphocytes (CD4 +)
They are the cells in command of the cellular immune response, in charge of coordinating the entire team. They are responsible for communicating with other lymphocytes and defensive cells to direct their action by activating or inhibiting them.
Cytotoxic T lymphocytes (CD8 +)
Cells highly specialized to recognize cells infected by the coronavirus and destroy them by injecting toxic proteins.
Regulatory T lymphocytes
They have a vital role, because they are the ones who decide when the "ceasefire" against the coronavirus occurs so that the immune response is proportionate and does not cause excessive damage on the battlefield, which is none other than the human body. If there were lymphocytes that went "crazy" during the fight against the coronavirus, to the point of not distinguishing friend from enemy, these cells would also take care of their elimination.
When the "alert" is activated in the human body that the coronavirus is present, the B lymphocytes they multiply rapidly and undergo many mutations to produce a high variety of these cells with greater or lesser effectiveness against the coronavirus. Those with the greatest ability to fight the virus are selected to differentiate themselves from plasma cells that will release thousands and thousands of antibodies per minute (mainly IgM and IgG) to neutralize the virus.
In addition to offering a precise and sophisticated response, exposure to the coronavirus generates memory lymphocytes (T and B). These memory cells are the 'war veterans', which will remain present in the human body in the long term to protect it from possible infections in the future. They are better indicators than antibodies to know the immunity of a person against the coronavirus.